An electromagnetic wave is typically composed of two types of waves, i.e., an electric wave and a magnetic wave, in which a higher frequency leads to a shorter wavelength and a higher energy level, and a lower frequency leads to a lower energy level. It is known that, while the electric wave is blocked by electrified metallic, conductive materials, the magnetic wave penetrates metallic, conductive materials, and, thus, a separate absorber is needed to block the magnetic wave. Since the electric and magnetic waves coexist, they are both extinguished when only one of both is removed
Therefore, a conductive metal is generally used for the purpose of shielding electric wave, and a magnetic material is generally used for the purpose of shielding magnetic wave.
The magnetic material is one or an alloy of two of iron-based metals, for examples, iron (Fe), nickel (Ni), cobalt (Co), and the like.
The decibel (dB) is a measure of the effect of electromagnetic wave shield, which is the ratio of electromagnetic waves intensity before and after shielding. The effectiveness of 20 dB means the reduction of the amount of electromagnetic waves to 1/10, and the effectiveness of 40 dB means the reduction of the amount of electromagnetic waves to 1/100. It is generally determined that the shielding effect is favorable at 30-40 dB or more. In order to protect electronic devices and human bodies from the harmfulness caused by the generation of electromagnetic waves, regulations have been tightened around the globe, and respective countries are tightening EMI regulations. Following this trend, a metal substrate is used, or a conductive coating or plating is applied to the substrate, for electromagnetic waves shield. The metal substrate has disadvantages in that it is not suitable for a complicated pattern process and it is heavy. Moreover, the method of substrate plating is not advantageous in view of the productivity due to complicated processes therefor, such as degreasing, etching, neutralizing, activating, accelerating, metal depositing, activating, and primary to tertiary plating steps. Moreover, shielding materials using a filler, such as carbon nanotubes, a metal powder, graphite, or ferrite, have been reported, but they show defects in dispersibility, processability, effectiveness of electromagnetic waves shield, and the like. Metal plating is applied to the filler in order to solve the disadvantages, but such a plating manner using a conductive powder is difficult for practical use due to delicate processes and high production costs.
As for recent techniques associated with electromagnetic waves shield, U.S. Pat. No. 5,827,997 discloses the complexation of nickel fibers, or carbon filaments plated with nickel through electroplating, with a polymer resin; US Patent Publication No. 2002/0108699 discloses the complexation of conductive fibers with a resin; Korean Patent Application No. 10-2009-0031184 discloses an electromagnetic waves shield film containing carbon nanotubes; Korean Patent Application No. 10-2006-0039465 discloses a method for manufacturing an electromagnetic waves shield film; Korean Patent Application No. 10-2000-0039345 discloses a material for electromagnetic waves shield using carbon nanotubes or carbon nanofibers; and Korean Patent Application No. 10-2009-0057726 discloses a method for preparing a polymer/carbon nanotube composite with excellent effectiveness of electromagnetic waves shield.
In addition, disclosed is a method for manufacturing a fabric for the purpose of electromagnetic waves shield by plating organic synthetic fibers. Japanese Patent Publication No. Hei 10-46443 discloses a fabric for electromagnetic waves shield. This patent is directed to a technique of manufacturing a shield fabric by silver-plating nylon, followed by weaving and arrangement, wherein the shield fabric has an effect of electromagnetic waves shield of 26-30 dB. Korean Patent Publication No. 2000-0034190 discloses that nylon short fibers or filaments were plated with silver, and the silver-plated fibers are mixed with other fabrics in a twisting step The above technique results in an effect of electromagnetic waves shield of about 26-38 dB.
Korean Patent Nos. 10-0929328 and 10-1213380 discloses a nickel-copper-nickel-plated fabric formed of organic fibers, which is used as a material for electromagnetic waves shield. This fabric shows a performance of electromagnetic waves shield of 54-62 dB. However, since the fabric acts like a metal plate after being plated, the magnetic shielding effect is shown by reflection, and thus the plated fabric is not differentiated from a metal plate of copper or the like. Moreover, when the plated fabric is used as a magnetic shielding material for a cellular phone and an electronic device, the damage to the electronic device by reflection waves and the harmfulness to the human body by diffraction of reflection waves are inevitable.
Throughout the entire specification, many papers and patent documents are referenced and their citations are represented. The disclosure of the cited papers and patent documents are entirely incorporated by reference into the present specification and the level of the technical field within which the present invention falls, and the details of the present invention are explained more clearly.